One of important technologies supporting the recent rapid technical progress is the development of equipment of information technology such as computers. It is not too much to say that the development of performance of the aforementioned information technology can be attained by the development of performance and/or integration of CPU (central processing unit) of information engineering equipment, i.e., ULSI (ultra large scale integrated) devices constituting CPU. As one of methods for drastically developing the performance and/or integration of ULSI devices, a method has been practiced which comprises developing the horizontal integration of ULSI, i.e., finely dividing elements, while developing the vertical integration of ULSI, i.e., multi level interconnection of ULSI.
The most important factor of the aforementioned multi level interconnection of ULSI is to secure the depth of focus (DOF) of optical lithography by which the wafer is exposed to light through a pattern for metal wirings such as interlayer dielectrics and metal wirings. In other words, it is required that the difference in height of concave and convex in the roughened surface be smaller than DOF of exposing light for patterning. To this end, leveling must be made with a high precision. In the process for forming a multi level interconnection, when there is a certain or higher difference in height of concave and convex in the interlayer dielectrics or metal wirings, it is made impossible to effect sufficient focusing or form a fine wiring structure.
The high precision leveling of a semi-conductor wafer can be difficultly attained by conventional SOG (spin on glass) or etching. As a substitute for these methods, there has been normally used super precision polishing such as CMP (chemical mechanical polishing). The leveling by CMP is carried out by using an abrasive (normally referred to as “slurry”, which will be used hereinafter) having a particulate material such as silica and alumina, mixed and/or dispersed in an alkaline or acidic chemically-corrosive aqueous solution and an elastic polishing material (hereinafter referred to as “polishing pad”) against the surface to be polished of an object to be leveled such as semi-conductor wafers.
Then, in order to facilitate the understanding of a role of each of sites in the polishing pad, the general behavior of polishing an object T to be polished by a polishing platen 60 using a polishing pad 50 which has hitherto been used will be described hereinafter by referring to FIGS. 8A, 8B and 8C. The polishing pad 50 is fixed onto the polishing platen 60 and provided for use (see FIG. 8A). The object T to be polished is held by a pressure head 62 disposed opposing to the polishing platen 60 (see FIG. 8B). By rotating and/or oscillating the object T to be polished, which is held by the pressure head 62, and pressing the polishing pad 50 which is fixed onto the polishing platen 60 and rotated at an arbitrary rate against the object T to be polished with a prescribed pressure while feeding a constant amount of a slurry from a slurry feed unit 64, the object T to be polished is polished (see FIG. 8C).
The polishing pad 50 which is used in such an embodiment is required to have (1) high local leveling properties against the object T to be polished (hereinafter referred to as “step height reduction”) and (2) high uniform leveling in wafer scale (entire wafer) (hereinafter referred to as “in-plane uniformity”). With respect to the step height reduction which expresses the local leveling properties (1), basically, if the hardness (rigidity) of the polishing surface in the polishing pad 50 is high, the so-called “step height reduction” becomes good due to preferential polishing of the convex in concave and convex of the object to be polished. On the other hand, however, since follow-up properties to waviness and mild concave and convex (generally called “nanotopography”) of the surface of the object to be polished are low, the in-plane uniformity is disordered. In contrast, since the in-plane uniformity (2) becomes good by bringing into contact with and/or polishing the waviness or warp of the surface of the object to be polished while applying a uniform load thereto, it is desired that the material of the polishing pad 50 is soft. That is, it was difficult to cope with both the step height reduction (1) and the in-plane uniformity (2).
In order to cope with both the step height reduction (1) and the in-plane uniformity (2), the polishing pad 50 was constructed such that a raw material having high hardness is used for the polishing surface which comes into contact with the surface of the object to be polished and that a raw material having low hardness, which enhances the follow-up properties to the object to be polished, is used in the side of the back surface of the polishing surface, namely, the side to be fixed onto the polishing platen 60. This has a so-called multilayered structure composed of a combination of two or more raw materials bonded to each other, such as a combination of a polishing layer 52 having high hardness on which a polishing surface is formed with a stress reduction layer 54 having low hardness as illustrated in FIG. 9.
The polishing pad 50 was generally provided for the actual polishing works in the following steps. That is, as illustrated in FIGS. 10A, 10B, 10C and 10D, (1) a first pressure-sensitive adhesive layer 56 composed of a substrate and a pressure-sensitive adhesive as in a double-sided pressure-sensitive adhesive tape is stuck on to the polishing platen 60 upon which the polishing works are carried out (see FIG. 10A); (2) the stress reduction layer 54 is stuck onto the pressure-sensitive adhesive layer 56 (see FIG. 10B); (3) a second pressure-sensitive adhesive layer 58 is stuck onto the stress reduction layer 54 (see FIG. 10C); and (4) the polishing layer 52 is ultimately stuck onto the second pressure-sensitive adhesive layer 58 (see FIG. 10D).
In order to attain the high in-plane uniformity (2), in sticking and/or fixing the resulting polishing pad 50 onto the polishing platen 60, it is required that the level in height on the surface of the polishing layer 52 is uniform and that an equivalent drag is outputted against a stress input such as a pressure in any portion of the surface of the polishing layer 52. However, when the pressure-sensitive adhesive layers 56 and 58, the polishing layer 52 and the stress reduction layer 54 are successively laminated (four times in this example) on the polishing platen 60, it is pointed out that the following problems are caused due to the thinness of the pressure-sensitive adhesive layers 56 and 58 and the difficulty in handling by adhesiveness.
That is, there are pointed out such problems that (1) it is difficult to uniformly stick the pressure-sensitive adhesive layer 56 or 58, or the level in height on the polishing surface does not become uniform because of the generation of air accumulation or non-uniformity of fine thickness generated due to a difference in stretching by the site of the pressure-sensitive adhesive layer 56 or 58; and that (2) the sticking of the pressure-sensitive adhesive layers 56 and 58, the stress reduction layer 54 and the polishing layer 52 is insufficient so that end portion is invaded by moisture or peels away during the polishing works. In the problem (1), the in-plane uniformity on the surface of the resulting object to be polished cannot be kept. With respect to the problem (2), the end portion in the polishing layer 52, etc. peels away or floats due to the invasion of moisture, whereby the profile control of an edge portion, etc. of a wafer as the object to be polished becomes difficult. The air accumulation is small in size, and after sticking of the polishing layer 52 and the stress reduction layer 54, it is covered by the respective layers 52 and 54. Accordingly, it cannot be observed from the outside, and the discovery is difficult (actually, the discovery of the air accumulation is judged only from the results regarding the polishing state on the surface of the object to be polished such as wafers). Also, since these problems cannot be surely avoided without skill of the sticking works, it is difficult to prevent such problems from occurring.
Further, it may be considered that the stress reduction layer 54 having high flexibility is stretched in the horizontal direction during sticking and/or fixing due to the contents of works. If a part of the stress reduction layer 54 is stretched in the horizontal direction, different flexibility is revealed depending upon the site of the stress reduction layer 54, resulting in making it impossible to attain sufficient in-plane uniformity.
Also, by integrating the polishing layer 52 with the pressure-sensitive adhesive layer 56 during producing the polishing layer 52 or by integrating the stress reduction layer 54 with the pressure-sensitive adhesive layer 58 during producing the stress reduction layer 54, it is possible to reduce the time of the lamination works on the polishing platen 60 into two times, thereby possibly reducing a probability of the generation of the aforementioned problems. Moreover, by employing a method in which in the production stage, not only the polishing layer 52 and the stress reduction layer 54 are laminated, but also a pressure-sensitive adhesive layer against the polishing platen 60 is laminated on the stress reduction layer 54 in advance, it may be possible to reduce a probability of the generation of the aforementioned problems, too. In this case, however, the lamination at the time of production is difficult, and the deterioration of the production yield leads to an increase of the production cost. Accordingly, this method could not be a fundamental dissolution method.